Negative-resistance effect in rubidium tetracyanoquinodimethane (Rb-TCNQ)

Nonlinear-conductivity phenomena, including negative-resistance and current-switching effects, have been observed in the radical-anion salt of rubidium tetracyanoquinodimethane (Rb-TCNQ) known as a spin-Peierls system. From the current and temperature dependences of infrared ${\mathit{a}}_{\mathit{g}}$ CN-stretching-vibration spectra, it is concluded that the observed nonlinear properties are not due to the Joule-heating effect but are attributable to the dynamics of soliton-type defects in the bond-ordered (dimerized) stacks of TCNQ molecules. The possible soliton-mediated transport mechanism in Rb-TCNQ is discussed, in parallel with previous discussions on similar nonlinear transport properties in mixed-stack organic charge-transfer crystals.